Phenols with persulfate

Phenols with a trifluoromethyl substituent on the ring are hydroxylated with potassium persulfate,167 while oxidation with chloric acid causes oxidation to quinonc and ring contraction together with incorporation of chlorine in the product.176 A detailed study of the oxidations of 2-, 3-, and 4-(trifluoromethyl)phenols shows that the oxidation with chloric acid at 5 to 10°C for 0.5 hours gives complex mixtures of products 1 77 5-chloro-l-hydroxy-4-oxo-5-(tri-fluoromethyl)cyclopent-2-enecarboxylic acid (12) being isolated as the major product from the 2-isomer. 

Fluonnatedphenols are usually oxidized to cyclohexadienone and benzoqui-none derivatives and to products of ring rearrangement and ring degradation Phenols with a tnfluoromethyl group at the nng are hydroxylated by potassium persulfate [57], whereas chloric acid causes oxidation to quinone, mg contraction, and incorporation of chlorine in the product [58] (equation 53)... 

The oxidation of phenol with potassium persulfate (K2S2O8) in an alkaline medium to p-hydroquinone is known as the Elbs persulfate oxidation. Elbs used ammonium persulfate for the oxidation of 2-nitrophenol (7.42) to 2-nitro-p-hydroquinone (7.43), but the potassium salt is commonly used for the hydroxylation of phenols. 

Reactions with persulfate and pyrosulfate. The persulfate (peroxy-dlsulfate Ion, S2O8 ) reaction, also known as the Elba persulfate oxidation, has been Important In synthesis of hydroxylated phenols. The method has occasionally been used for synthesis of 0-sulfate conjugates. For example, 4-hydroxy-2-nltrophenyl sulfate was obtained when 3-nltrophenolate was stirred with potassium peroxydlsulfate at room temperature for 2 days (91,). The persulfate reaction has been used for the sulfation of various phenols and aromatic amines however the yields are usually low to moderate (77 ). The sulfate group Is preferentially Introduced In the 4-posltlon of phenols and In the 2-posltlon of aromatic amines but If these positions are blocked substitution at the 2- and... 

Figure 28.21 The reactions of R u (11) pby 3 + are catalyzed by light at 452 nm that begins by forming an excited state intermediate. In the presence of persulfate, a sulfate radical is formed concomitant with the oxidative product Ru(III)bpy33+. This form of the chelate is able to catalyze the formation of a radical on a tyrosine phenolic ring that can react along with the sulfate radical either with a nucleophile, such as a cysteine thiol, or with another tyrosine side chain to form a covalent linkage. The result of this reaction cascade is to cause protein crosslinks to form when a sample containing these components is irradiated with light.

When aromatic amines react with potassium persulfate in alkaline aqueous solution at room temperature in the absence of a catalyst, they are converted to the corresponding phenol . Behrman has studied the ortho-para ratio in this reaction and found that the ortho product predominates over the para product (in contrast with the Elbs reaction)... 

Electron-rich arenes, for example phenols, anisoles, and arylamines, can be hy-droxylated with potassium persulfate in basic media [29]. Hydroxylation of phe-... 

Looker et al used a modification of the Bbs persulfate oxidation procedure in which tetraethyl-ammonium hydroxide was used as the base in their synthesis of S,8-4uinoflavone. The phenol (65) was oxidized to the hydroquinone, primetin (66), which upon further oxidation with LTA affwded S,8-flavo-quinone (67) in 34% overall yield (Scheme 24). 

The Elbs persulfate oxidation procedure was used by Bach and coworiters at an early stage of their syndiesis of model compounds related to fipedericamycin A. Thus the phenol (59) gave 2,5-dihydroxy-4-methoxybenzoic acid (60) in modest yield (30%). This was then transformed in several steps to the isobenzofiiranone (61). Generation of the isobenzofiiran (62) in situ and Diels-Alder reaction of this with the enedione (63) gave, after loss of the trimediylsilyl group, the desired compound (64 Scheme 23) in 62% yield from the isobenzofuranone (61). 

Peroxidic initiators, like dibenzoyl peroxide, are too reactive with phenolic and aminic moieties and can be applied only exceptionally [50], Inorganic peroxides, like potassium persulfate, were used for emulsion polymerization of functionalized monomers [51]. Phase transfer catalysis may be also applied using persulfate initiation. To circumvent problems with the peroxide initiation, 4,4 -azobis(4-cyanovaleric acid), a water soluble initiator, was successfully used [48]. 

A key step in the synthesis of the simple aromatic bisphenol tetrangulol (3) by Brown and Thomson [18] was a Michael-type cyclization of a phenol to the chloronaphthoquinone moiety (Scheme 3). The starting material 8, connecting the naphthoquinone and the protected phenol, was prepared by an interesting radical alkylation of the chloronaphthoquinone 6 with a carboxylic acid 7 in the presence of silver ions and persulfate with concomitant decarboxylation (Torsell reaction [19]) to yield the dihydrobenzo[a]anthraquinone 9. The synthesis of tetrangulol (3) was concluded by dehydrogenation in boiling nitrobenzene. 

Oxidations with sodium persulfate are markedly catalyzed by silver ions the actual reagent is presumed to be SjOg Ag". Toluene is oxidized to benzaldehyde (50% yield) together with coupled products, and benzyl alcohol is oxidized to benzaldehyde (75% yield). Phenols are oxidized to resinous polyphenols. ... 

The further oxidation of phenol may also result in the formation of catechol, C,iH4(OH) (1 2). The transformation may be effected by fusion with sodinm hydroxide.85 The snbstance may also be obtained by oxidizing benzene with hydrogen peroxide in the presence of ferrous sulfate88 and by reducing o-benzoquinone with aqueous sulfurous acid in the cold.81 Quinol may be prepared from phenol by oxidation with potassium persulfate in alkaline solution.38 It can also be obtained directly from benzene by the electrolytic oxidation of an alcohol solution to which... 

One simple example of much-preferred para attack is in the Elbs persulfate oxidation of phenol. The reaction is usually written as the combination of a phenoxy radical 7.123 with the persulfate radical anion 7.126, but it could be phenoxide ion undergoing electrophilic substitution in any event, para attack is substantially favoured over ortho attack.1... 

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